Generally, a magnetic-type position detector detects a change in the position of a detection object relative to a reference part. For example, a position detector disclosed in a patent document 1 (i.e., Japanese Patent Laid-Open No. JP-A-H08-292004) is configured (i) to form a closed magnetic circuit with two magnets and two yokes. The position detector also has a magnetic flux density detector disposed inside of the closed magnetic circuit within a gap between the two yokes. Each of the two yokes has a flat board shape, and the width of the gap between the two yokes is constant along the longitudinal direction of the yoke and at all positions throughout the entire longitudinal length of the two yokes. The two flat board shape yokes generally bind or sandwich the two magnets. That is, one of the two magnets is positioned between a first end of each yoke and the other one of the two magnets is positioned between a second end of each yoke.
Magnetic fluxes flowing out from an N pole of one magnet are categorized into three types, a return magnetic flux that flows through one of the two yokes and flowing from one magnet to the other magnet, a spill magnetic flux that flows from one yoke into the gap between the two yokes and flows to the other yoke, and a direct magnetic flux that flows directly without passing through any yoke into the gap between the two yokes and flows to an S pole. The magnetic flux density detector detects the following two types of flux flowing therein, that is, either one or both of the spill magnetic flux and the direct magnetic flux. The density of the magnetic flux passing through the magnetic flux density detector changes according to a position of the magnetic flux density detector relative to the yoke. The position detector detects a position of the detection object based on the density of the magnetic flux which is detected by the magnetic flux density detector.
In the position detector disclosed in the patent document 1, the density of the magnetic flux which passes through a magnetic flux density detector steeply changes due to the influence of the direct magnetic flux flowing in an end portion of the gap between the two yokes. Therefore, the relationship between the position of the detection object and the output signal from the magnetic flux density detector (i.e., a position-output correlation) is observed as having a linear relationship when the magnetic flux density detector moves at or around a center part of the gap relative to the two yokes, but the position-output correlation departs from such linear relationship when the magnetic flux density detector moves at or around the end portions of the gap relative to the two yokes. In other words, the output signal from the magnetic flux density detector is not sufficiently linear.